1. Field of the Invention
The present invention relates to developing devices, image forming apparatuses, and image forming systems.
2. Description of the Related Art
(1) There are known image forming apparatuses that are provided with, for example: an image bearing body for bearing a latent image; a developing device for developing the latent image borne by the image bearing body using developer; a transferring device for transferring, onto a medium, the developer image that has been made visible by the developing device developing the latent image with the developer; and a fusing device for fusing, to the medium, the developer image that has been transferred onto the medium using the transferring device. When an image forming apparatus of this type receives image signals etc. from an external device such as a host computer, it positions the developing device at a developing position which is in opposition to the image bearing body. The image forming apparatus then forms a developer image by developing the latent image borne by the image bearing body with the developer contained in the developing device, transfers the developer image onto a medium, and fuses the image to the medium to thereby form an image on the medium.
In order to achieve the above-mentioned function of developing the latent image formed on the image bearing body, the developing device of the type described above is provided with, for example, a developer bearing body for bearing the developer, and a charging member for charging the developer borne by the developer bearing body by abutting against it. Such a developing device charges the developer borne by the developer bearing body using the charging member, and develops the latent image borne by the image bearing body with the charged developer.
Further, the developer used in such an image forming apparatus contains a sufficient amount of release agent. Therefore, in consideration of maintainability etc., the fusing device of the image forming apparatus is not provided with oil for preventing the medium from adhering to the fusing device when the developer image is fused to the medium. (Refer, for example, to JP 2003-107905A.)
Incidentally, in such an image forming apparatus, a phenomenon called “white spots” may occur when the developer including the release agent is electrically charged by the charging member and the charged developer is used for developing the latent image borne by the image bearing body. Occurrence of such a phenomenon may cause deterioration in the images that are finally obtained.
(2) There are also known image forming apparatuses that are provided with, for example: an image bearing body for bearing a latent image; a developing device for developing the latent image borne by the image bearing body using developer; and a turnable turning body to which the developing device is attached. When an image forming apparatus of this type receives image signals etc. from an external device such as a host computer, it positions the developing device at a developing position, which is in opposition to the image bearing body, by turning the turning body about its axis of turning. The image forming apparatus then forms a developer image by developing the latent image borne by the image bearing body with the developer contained in the developing device, and transfers the developer image onto a medium to thereby form an image on the medium.
In order to achieve the above-mentioned function of developing the latent image formed on the image bearing body, the developing device of the type described above is provided with, for example, a developer container for containing the developer, a developer bearing body for bearing the developer contained in the developer container, and a charging member for charging the developer borne by the developer bearing body by abutting against it. Such a developing device charges the developer borne by the developer bearing body using the charging member, and develops the latent image borne by the image bearing body with the charged developer.
Further, in such an image forming apparatus, the developer in the developing device, which is attached to the turning body, is stirred as the turning body is turned, and accordingly, the developer is maintained in a suitable state. Therefore, the developer container is not provided with a stirring member for stirring the developer. (Refer, for example, to JP 2000-347499A.)
However, in situations where an image is continuously formed on a plurality of sheets of media with developer of a single color (for example, monochrome) using the image forming apparatus described above, the same developing device will be used for the development for a long time, and thus, the turning body will not be turned for a long time.
If, in a state where the turning body is not turned for a long time, development is carried out continuously with the developer borne by the developer bearing body without the developer being stirred, then the amount of charge of the developer in the vicinity of the developer bearing body, among all of the developer contained in the developer container, becomes excessively large. That is, developer with a significantly different amount of charge will co-exist in the developer container (and polarization in the characteristics of the developer will occur). This will bring about electrostatic agglomeration of the developer when the developer is mixed. The developer that has caused electrostatic agglomeration may spill when, for example, the developer that has been mixed is used for developing the latent image.